Shielded structure for radiation treatment equipment and method of assembly

ABSTRACT

A structure that can be partially assembled at one location, transported to a site in modules, and then fully assembled into a structure suitable for housing a therapeutic radiation source is disclosed. The modules include reinforced walls that are filled with radiation shielding fill material to form a barrier around a central treatment area. Additional modules are placed over the first set of modules and form a barrier above the treatment room. A door with a selectively retractable threshold provides access to the treatment room. The module including the radiation equipment is included in removable portions so that the radiation equipment can be removed and replaced. The modules also form a patient waiting room and control area separated from the treatment by the barrier.

FIELD OF THE INVENTION

[0001] The present invention relates generally to structures andportions thereof for housing radiation sources and shielding humansworking near those sources. More particularly but not exclusively thepresent invention relates to a structure and method for constructing astructure for housing a therapeutic radiation source.

DESCRIPTION OF THE RELATED ART

[0002] Radiation is used in the diagnosis and treatment of patients invarious ways. However, while controlled doses can be beneficial to apatient, those working with the radiation or merely in the surroundingarea need to be protected from the harmful effects of the radiation.Accordingly, shielding is traditionally provided to isolate theradiation source from those in the surrounding area and provide someprotection from the levels associated with normal use of the equipmentand also, to some extent, to accidents with the radiation equipment.

[0003] However, the need for shielding, which is traditionally providedby concrete walls or mounds of dirt, severely limits the feasibility ofradiation treatment centers in many locations. This limitation is due atleast in part to the high cost of constructing these buildings and tothe inability to easily disassemble or remodel the centers toaccommodate new development of the surrounding structures and land.Accordingly, new apparata and techniques are needed for rapidly andeconomically constructing radiation treatment centers to allowfacilities to be located wherever patients needs require suchfacilities. Various embodiments of the present invention address theseand other needs.

SUMMARY OF THE INVENTION

[0004] The present invention provides a novel structure that can bepartially assembled at one location, transported to a site, and thenfully assembled into a structure suitable for housing a therapeuticradiation source and treating patients therewith. The structure caninclude means for containing a radiation fill material to provide abarrier around and above a central treatment area that includes a pieceof radiation equipment and the structure includes means for selectivelypermitting access to the treatment area. The access means can include ashielded door with a retractable threshold that retracts upon openingthe door and raises when the door is closed to restrict radiation fromescaping through the doorway. The structure can also be adapted to allowthe radiation equipment to be removed and replaced after the barrier isconstructed, without removing any substantial portion of the barrier.

[0005] In one embodiment there is provided a modular structure forhousing a radiation source comprising a plurality of free standingtransportable modules connected to form a central treatment area and abarrier substantially surrounding the central treatment area, thecentral treatment area adapted for human occupation and to contain atherapeutic radiation source, the modules comprising a support framestructure and at least one wall, the barrier including first and secondspaced apart rigid walls and a quantity of radiation shielding fillermaterial contained between the first and second walls, the quantity offiller material sufficient to substantially reduce the measurableradiation level outside the central treatment area when a radiationsource is placed in the central treatment area. In various refinementsat least two of the modules include portions of the first and secondspaced apart rigid walls, the portions defining a channel comprising aportion of the barrier wherein the channels in the at least two modulesare adjacent and substantially aligned. The adjacent channels are influid communication such that radiation shielding filler materialprovided into one channel can flow into the adjacent channel. Themodular structure includes a second plurality of free standingtransportable modules connected to form a roof barrier above the centraltreatment area, the roof barrier comprising a rigid floor supporting aquantity of radiation shielding filler material above the centraltreatment area. The second plurality of modules includes portions abovethe barrier formed by the first plurality of modules, the portions abovethe barrier being in fluid communication with the barrier and includinga quantity of radiation shielding filler material. Portions of theplurality of modules define an area outside the central treatment areaand the barrier, the outside area is adapted to form rooms suitable forhuman occupation. The first and second plurality of modules each have alength not exceeding about 53 feet, a width not exceeding about 14 feet,and a height not exceeding about 13 feet 6 inches. Each of the moduleshave a major axis defined along their length where the major axes of thefirst plurality of modules are substantially parallel to each other andthe major axes of the second plurality of modules are substantiallyparallel to each other.

[0006] There is also disclosed a novel method of constructing astructure for housing a radiation source. The method includes forming acentral treatment area sized and configured for human occupation and tocontain a therapeutic radiation source, connecting a plurality offree-standing transportable modules to form a barrier zone substantiallysurrounding the central treatment area, the barrier zone defined by atleast first and second spaced apart rigid walls comprising portions ofthe plurality of modules, delivering a quantity of radiation shieldingfiller material to the barrier zone to form a barrier substantiallysurrounding the central treatment area, the quantity of filler materialsufficient to substantially reduce the measurable radiation leveloutside the central treatment area when a radiation source is placed inthe central treatment area. In various refinements the method furtherincludes placing portions of at least two of the plurality of modulesforming the barrier zone in fluid communication such that radiationshielding filler material can flow between the portions, connecting asecond plurality of free standing transportable modules to the firstplurality to form a roof barrier zone over the central treatment area,delivering a quantity of radiation shielding filler material to the roofbarrier zone to form a roof barrier above the central treatment area,and placing a portion of the roof barrier in fluid communication withthe barrier such that radiation shielding filler material provided intothe roof barrier can flow into the barrier. A portion of the barrierzone is formed with walls that include rigid reinforcing members on thewalls and rigid support members mounted between the walls. In stillfurther refinements the plurality of modules have a longer side and ashorter side, and the structure is formed by connecting the long side ofone of the plurality of modules to the long side of another of theplurality of modules to form the central treatment area. Human access isprovided to the central treatment area from an area outside the barrierthrough a door in one of the modules.

[0007] There is also provided a novel apparatus for forming a radiationtreatment center comprising a plurality of free standing modules eachcomprising a support frame and at least two spaced apart rigid wallsdefining a channel between the walls, the modules each having outerdimensions generally defining a rectangular solid having a major axis,wherein the modules are adapted to be connected to each other to form abarrier zone substantially surrounding a central treatment area, thebarrier zone comprising the channels of the modules and wherein thechannels of at least two of the modules are in fluid communication suchthat radiation shielding filler material provided into one channel canflow into the adjacent channel, and a second plurality of free standingmodules at least one of which comprises a reinforced floor portion, thesecond plurality of modules adapted to be placed on top of and connectedto the first plurality of modules with the reinforced floor portionsabove and substantially covering the central treatment area, the secondplurality of modules having portions that would be aligned over and influid communication with the barrier zone such that radiation fillermaterial provided into the second plurality of modules could flow intothe barrier zone.

[0008] There is also provided a novel transportable module for forming astructure comprising a free standing transportable frame structuredefining a bottom surface, a top surface and at least first and secondspaced apart side surfaces, a pair of spaced apart reinforced rigidwalls mounted to the frame and defining a channel space between thewalls, rigid supports mounted in the channel space between the walls toresist lateral forces acting from inside the channel to force the wallsapart, wherein a substantial portion of the channel space between thewalls does not contain a ceiling or a floor such that the channel spaceis open at its top and bottom such that granular fill material can beprovided into the channel space from above the top surface and entirelyfill the channel space, and wherein the module is capable of beinglifted by its ends by a standard container mover without substantialdeflection to facilitate construction of a structure comprising aplurality of modules.

[0009] There is also provided a transportable module for forming astructure comprising a free standing transportable frame structuredefining a bottom surface, a top surface and at least first and secondspaced apart side surfaces, a pair of spaced apart reinforced rigidwalls mounted to the frame and defining a channel space between thewalls, rigid supports mounted in the channel space between the walls toresist lateral forces acting from inside the channel to force the wallsapart, wherein a substantial portion of the channel space between thewalls does not contain a ceiling or a floor such that the channel spaceis open at its top and bottom such that granular fill material can beprovided into the channel space from above the top surface and entirelyfill the channel space, and wherein the module is capable of beinglifted by its ends by a standard container mover without substantialdeflection to facilitate construction of a structure comprising aplurality of modules.

[0010] There is also provided an apparatus for selectively blockingradiation through a doorway comprising a door and a retractablethreshold adjacent the door, wherein the door and the retractablethreshold each comprise radiation shielding material, a liftingmechanism for raising the threshold when the door is closed and loweringthe threshold when the door is open, wherein the threshold blocksradiation leakage under the door when the door is closed and permitssubstantially unobstructed access through the doorway when the door isopen. In further refinements a portion of the threshold is above thebottom of the door when the door is closed, and the threshold retractssubstantially under its own weight when the door is opened.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of an assembled modular structureaccording to one embodiment of the present invention.

[0012]FIG. 2 is an exploded, perspective view in partial section of themodular structure of FIG. 1.

[0013]FIG. 3 is a top plan view of the first floor level of thestructure of FIG. 1.

[0014]FIG. 4 is a top plan view of the second floor level of thestructure of FIG. 1.

[0015]FIG. 5 is a top plan view of a first pod in the embodiment ofFIGS. 3 and 4.

[0016]FIG. 5A is a side elevational view in full section of the FIG. 5pod.

[0017]FIG. 5B is a partial enlarged top plan view in full section ofadjacent wall segments and a wall support.

[0018]FIG. 6 is a top plan view of a second pod from the embodiment ofFIGS. 3 and 4.

[0019]FIG. 6A is a side elevational view in full section of the FIG. 6pod.

[0020]FIG. 6B is a top plan view in full section of the FIG. 6 pod.

[0021]FIG. 7 is a side elevational view in full section of a third podfrom the embodiment of FIGS. 3 and 4.

[0022]FIG. 8 is a top plan view of a sixth, second floor pod from FIG.4.

[0023]FIG. 8A is a side elevational view in full section of the FIG. 8pod.

[0024]FIG. 8B is an end elevational view in full section of the FIG. 8pod.

[0025]FIG. 9 is a top plan view of a ninth, second floor pod.

[0026]FIG. 9A is an end elevational view in full section of the FIG. 9pod.

[0027]FIG. 10 is a top plan view in full section of an alternativearrangement for a third pod in the embodiment of FIGS. 3 and 4.

[0028]FIG. 11 is a side elevational view in full section of the FIG. 10pod.

[0029]FIG. 12 is a top plan view of an alternative arrangement for aninth, roof pod in the embodiments of FIGS. 3 and 4.

[0030]FIG. 13 is a side elevational view in full section of the FIG. 12pod.

[0031]FIG. 14 is a front elevational view of the lifting mechanism forthe retractable threshold.

[0032]FIG. 14A is a side elevational view in full section of thethreshold of FIG. 14 in the raised position adjacent the closed vaultdoor.

[0033]FIG. 15A is an end elevational view in partial section of arepresentative connection between the lower rails forming the long sidesof adjacent pods.

[0034]FIG. 15B is a top plan view in partial section of a representationconnection between the corner posts of adjacent pods.

[0035]FIG. 15C is a top plan view in partial section of a representativeconnection between interior wall segments of adjacent pods.

[0036]FIG. 15D is an end elevational view in partial section of an upperrail connection between adjacent pods.

[0037]FIG. 15E is a top plan view in partial section of an adjacent podconnection to a door gusset portion of a pod.

[0038]FIG. 15F is a side elevational view in partial section of arepresentative connection between an end of a roof pod with the outerwall and frame of a footprint pod.

[0039]FIG. 15G is a side elevational view in partial section of arepresentative connection of the load support beams in the roof podswith the roof support structures in the footprint pods.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0040] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated structures and methods, andsuch further applications of the principles of the invention asillustrated therein being contemplated as would normally occur to oneskilled in the art to which the invention relates.

[0041] Turning now to FIGS. 1 and 2, structure 40 for housingtherapeutic radiation equipment is depicted. Structure 40 is a modularunit that is assembled to form a radiation therapy vault room 50, andcan be delivered to a site in sections with all equipment and finishingsin place. The individual sections 101-110, herein referred to as pods ormodules, are preferably each capable of being shipped by rail, ship, oroverland freight and of being assembled together using commonlyavailable equipment such as cranes or container movers. In addition, thepods are preferably built to meet the US Department of Transportation(DOT) regulations concerning travel on the interstate highways.Currently, the DOT code includes a weight limitation of 85,000 poundsincluding the tractor and the trailer along with size limitations of awidth not exceeding 14 feet, a height not exceeding 13 feet 6 inches,and a length not exceeding 53 feet.

[0042] Referring now to FIGS. 1-4, as assembled, the modular structure40 includes a total of ten pods and has two or more interior rooms. Oneroom 50 is adapted to contain equipment capable of being used to performradiation therapy, and the other room 60 is adapted to be used as acontrol area suitable for use by a radiation therapist operating theequipment contained in room 50. Either room 50 and/or room 60 can befurther divided into additional rooms, for example to provide a patientwaiting area or multiple treatment areas. The modular unit 40 also has aseries of interior and adjoining containers that can be filled withradiation shield material to form a barrier 70 around the treatment area50 and a roof barrier 80 above the treatment area 50. The radiationshield material can be a flowable and/or granular material such as sand.

[0043] Five pods (pods 101-105 referred to as the footprint pods) areused to form the footprint of the building 40 (see FIG. 3). Anadditional five pods, (pods 106-110, referred to as the roof pods) areplaced on top of and perpendicular to the five footprint pods (see FIG.4). Of the five roof pods, four pods (pods 106-109, referred to as the“roof shielding pods”) give additional radiation shielding in thevertical direction by way of the roof barrier 80, whereas pod 110 isprimarily used as a storage area.

[0044] Pods 102, 103, and 104 connect together to form the interiorworkspace or therapy room 50. These pods align to form a continuousunobstructed space, for example a space measuring approximately 24 feetwide and 20 feet in length. Pod 103 serves as the center footprint pod,containing most of the medical equipment, and has quick connections forelectrical power and a mounting platform for the medical equipment 600.A weather seal can be incorporated along the joints between all of thefootprint pods as well.

[0045] Pod 101 is attached to the exterior side of pod 102, and pod 105is attached to the exterior side of pod 104. These two pods (pod 101 andpod 105), together with portions of pods 102-104, receive the radiationshielding material to form the barrier 70. The barrier 70 extendssubstantially around all sides of the room 50, with pod 102 including adoorway to permit access to the treatment room 50. The roof shieldingpods (pods 106-109) are placed above and connected to the five footprintpods, at least pods 101 and 105 including roof support structures 120,122 to support the load of the roof pods. Pods 106-109 are used forradiation shielding purposes whereas pod 110 can be reserved to housethe electrical equipment, telephone equipment and other utilities.

[0046] For assembly a suitable foundation, such as a concrete slab, isfirst created. The foundation is then leveled and the first of thefootprint pods, for example pod 103, is placed on and anchored to thefoundation. The remaining footprint pods are then sequentially placedand attached to their respective adjoining pod(s) and to the foundationand a weather seal is formed between adjoining pods and the foundation.A portion of the radiation shielding material can then be pumped intothe containers of the various footprint pods to form the barrier 70.

[0047] Either before or after filling the containers of the variousfootprint pods with the radiation shielding material, the roof pods canbe placed on and attached to the five footprint pods. A weather seal canthen be made between the footprint pods and the roof pods as well asbetween adjoining roof pods. The modular structure 40 can then be filledwith the shielding material. Electrical, water and sewage are thenconnected to the modular unit. By providing the structure 40 as amodular unit, the assembly time from the pods' arrival on site to thefinished structure 40 can be minimized. It is envisioned that theformation of the structure 40 would only take on the order of a few(3-4) days, greatly decreasing the time and cost traditionally needed toconstruct a radiation treatment facility.

[0048] Having described the general layout of the pods and the formationof the structure, more particular features of the individual pods areconsidered. Each of the pods can be built with an outside dimensiongenerally the same as a standard eight by forty foot extended height(9′6″) shipping container. The pods are transportable, which means thatthey each meet DOT regulations and codes for overland freight.Optionally, each can also be rigidly constructed to be capable of beinglifted from the end points by a container mover. They can also be formedto be stacked five pods high, for example during transit in an oceangoing vessel. The pods can also be constructed to be shipped and stackedwith other container types where the other containers having a grossweight of 96,000 pounds each. The shipping weight of each pod, includingany additional shielding or support structures or other integratedcomponents, but without the radiation shielding fill material, is mostpreferably consistent with DOT shipping regulations for moving by truckwithout special permitting.

[0049] More particularly, each of the pods is constructed of a steelexterior skeleton or frame 90 (see FIG. 5) that generally defines theouter edges of the pod. The frame 90 is preferably formed of squarechannel and flat plate steel welded, bolted, or otherwise securelyfastened together to form the boundaries of the generally rectangularsolid shape of the pod. “C” shaped beams 92 form the longer lower sidesof the rectangular footprint of each pod, with angled rails 96 formingthe upper borders. Rectangular posts 94 form the four side edges betweenthe upper 96 and lower 92 rails. Where present, wall segments aresecured to the interior of the skeleton or frame 90 (for example bywelds or rivets) with any wall or floor segments intended to contain theradiation fill material formed of flat sheet steel. Other wall, floor,or ceiling segments can be mounted to the frame and formed of anysuitable building material. Where, a wall, floor, or ceiling segment isnot present in any individual pod, or is of non-load bearingconstruction, structural rigidity of the pod can be increased to thedesired level by providing rigid support members between segments offrame 90.

[0050] Turning now to FIG. 5, pod 101 is constructed in two regions, afill area 210 and a finishable area 212. The fill area 210 forms a partof the barrier 70 and does not contain a floor so that the radiationshielding material provided into area 210 can be substantiallycontinuous to the foundation. Area 210 also does not have a ceiling. Thefinishable area 212 has no side wall along the section that joins to pod102, but a floor can be provided. The interior of area 212 can besuitable for interior finishing of the floors, wall and ceiling to makeit a patient area.

[0051] Fill area 210 is defined by oppositely disposed vertical insideand outside walls 214 and 216 and side walls 215 and 217. Optionally,inside wall 216 is at least partially absent at the portion that adjoinsto the barrier regions of pod 102 to permit fill material to flowbetween the adjacent barrier regions. Each of the walls are rigid andcan be reinforced to contain the load of the radiation fill materialwithout substantial deflection. Each of the walls are constructed offlat panel steel and have a plurality of vertically oriented supports202 welded or otherwise affixed thereto at spaced intervals along thewall length. Where more than one wall panel 510 is required to span thelength of a wall, the supports 202 also serve to connect adjacent panelsof the wall material. (See FIG. 5B) The supports are elongated pieceswith a “L” shaped cross section having one flat portion 202 b welded orriveted to adjacent steel wall sections 510 and a second flat portion202 a generally perpendicular to the wall panels 510. The perpendicularextending portions of supports 202 are tapered such that they arethicker at the bottom of the walls where the largest lateral force fromthe fill material can be expected. (See FIG. 5A)

[0052] For additional lateral support in the radiation fill area, rigidhorizontal supports 204 are also affixed generally between the topportions (204 a in FIG. 5A) and bottom portions (204 b) of the walls, orequivalently directly to the frame structure 90. Steel supports 204extend between walls 216 and 214 and at angles between wall 215 andwalls 216 and 214 and between wall 217 and walls 214 and 216.

[0053] In typical use the lateral force on the walls of container 210could be 170,000 pounds at a pressure of approximately 6.4 pounds persquare inch. The maximum lateral force could be increased by the weightof the fill from the roof pods on the top of pod 101, and the wallmaterial, thickness and supports should be chosen to support the load.

[0054] It is to be understood that the actual load and pressuresexperienced by the various portions of the pods might vary by a factorof 10 or more in either direction from any of the estimated loadspresented herein. Among other things, these exemplary loads can beexpected to depend on the density of the fill material. In addition, thewalls and/or associated supports can be designed to withstand severaltimes the expected load for any particular application.

[0055] In addition, access ports can be placed at appropriate intervalsalong the walls of container 210 to allow a pump or other suitable fillmechanism to fill and empty the container of the shielding material.Alternatively the fill portion 210 can be filled and emptied through itsopen top and bottom.

[0056] Pod 101 is constructed to include central region 218 in whichadditional shielding, such as a lead plate, may be added. Region 218 canbe, for example, eight feet wide by 9.5 feet high and seven inches thickand located near the center of pod 101 or wherever relatively largerradiation levels could be expected (for example depending on theorientation and use of the medical device in room 50). A variety ofshielding materials may be used for this purpose and they may be apassive or a structural part of the pod. Diagonally extending rigidlateral supports 219 are provided to accommodate any additional weightof the additional shielding material.

[0057] The roof shielding pods will be placed on top of pod 101perpendicular to the footprint pods and filled with radiation shieldingmaterial. The weight of the filled roof shielding pods could be as highas 250,000 pounds each, all of which load can be substantially supportedby pod 101 and pod 105. Pod 101 includes roof supports 120 as a portionof the wall to hold one half of the weight of the four roof shieldingpods and transfer the weight to the foundation below. As discussedabove, the majority of portion 210, like similar fill areas of the otherfootprint pods, has an open top to allow fluid communication with theroof pods.

[0058] Turning now to FIG. 6 and with continued reference to FIGS. 3 and4, pod 102 is adjacent to pod 101. Pod 102 also has several regionswithin it. Region 220 is eight feet wide by six feet deep and the fullheight of the pod. It is located in the rear of the pod and forms aportion of the barrier 70. When filled with radiation shielding materialthe weight of the fill in portion 220 might be 44,0000 pounds withapproximately 6.4 pounds per square inch of weight. Area 220 does notcontain a floor or ceiling so that the shielding material can besubstantially continuous to the foundation and to the roof barrier. Thelateral force on the side walls might be 34,000 pounds, and the maximumlateral force could be increased by the weight of the fill from the roofshielding pods on the top of this pod. The wall material, thickness andsupports should be chosen to support these exemplary loads or the loadfor any particular application.

[0059] Area 221 contains a vault door 130. Door 130 is five feet wide byseven and one half feet high. The door is a hollow steel door eightinches thick. The hollow portion of the door can be filled with fourinches of lead, and 3.8 inches of boridated polyethylene. It isenvisioned that the weight of the door with its frame and additionalwall shielding adjacent to the frame will be approximately 10,000pounds.

[0060] Door 130 is located between areas 221 a and 221 b that, like area220, are adapted to receive the radiation fill material. Door 130separates the control room 60, or patient area 65 (of which area 222 isa part) from the treatment room 50 allowing access back and forth. Area222 also includes a standard exterior door consistent with localbuilding codes to allow access to the patient area 65.

[0061] Portions 223 and 222 are suitable for interior finishing of thefloors, walls and ceiling to make it a patient area. They can also haveprovision for a quick connect for electricity, for lighting and tooperate the vault door 130.

[0062] Pod 102 also includes a door jam mechanism to be used foradditional protection against radiation out leakage in the event thereis no maze shielding walls (as is traditionally provided at the entranceto radiation rooms) or when the maze is not sufficient to adequatelyblock radiation leakage. The mechanism includes a lifting mechanismcoupled to a retractable threshold 132 that pops up to be adjacent todoor 130 upon the closing of the vault door 130, effectively blockingradiation leakage. The threshold 132 retracts, returning to its placeupon the opening of the door. The lifting mechanism can include a pairof hydraulic cylinders 134, 136 (see FIGS. 14 and 14A) of the type knownas pancake cylinders. A gear or lever assembly actuatable under theforce of the closing door could also be used. The lifting mechanism(cylinders 134, 136) are electronically or hydraulically activated by aswitch that senses whether the door is open or closed, for example byprovision of a pair of cooperating magnetic sensors mounted on the doorand door jam respectively. Preferably the threshold 132 iselectronically interlocked with a pair of door switches and/or with theradiation machine 600 such that the machine 600 is prohibited from beingin use when the door 130 or the threshold 132 are in a position to allowradiation leakage from the room.

[0063] The door jam is normally hidden and level with the floor so asnot to be a hazard for persons walking across it. When the vault door130 is closed, cylinders 134, 136 raise the threshold above the bottomof the door to block radiation leakage under the door. In the event ofany emergency, the pop-up mechanism of the door jam can work inconjunction with the vault door and/or be actuated manually. Forexample, the door jam can require electrical power to stay in the raisedposition such that in the event of a power failure, the threshold 132automatically retracts under its own weight. The door jam is anenhancement to any radiation therapy center, as most centers do notutilize any type of a seal under a vault door. The door jam is notrestricted to the use of the modular system and can be retrofitted toany type of door as would occur to those of skill in the art whenpresented with the present disclosure.

[0064] Pod 103 is located in between pod 102 and pod 104. It is to bebuilt with an outside dimension the same as an eight by forty-footextended height (9′6″) shipping container. When finished, it can meetDOT regulations and codes and be capable of being lifted from the endpoints by a container mover.

[0065] As illustrated in FIG. 7, pod 103 is divided into four sections.Sections 302 and 306 are fill areas that do not contain a ceiling or afloor and are open to the fill areas of the adjacent pods. The lateralforce on the side walls might be 34,000 pounds, where the maximumlateral force could be increased by the weight of the fill from the roofshielding pods on the top of this pod. The wall material, thickness andsupports should be chosen to support this exemplary load or the loaddictated by any particular application. Access ports can be placed atappropriate intervals to allow a vacuum pump to fill and empty thecontainer of the shielding material.

[0066] Additional shielding panels 303 and 305 are added between areas302 and 304 and between areas 304 and 306. Steel may be used for thispurpose, and it may be a passive or a structural part of the pod.

[0067] There is no side wall on areas 304 and 308 adjacent to pods 102or 104. Pod 103 is capable of being connected to pods 102 and 104 with awatertight weather seal and it has provisions to anchor it to thefoundation in accordance with standard building codes for a mobilebuilding. Areas 304 and 308 are suitable for interior finishing of thefloors, walls and ceiling to make it a patient area.

[0068] Pod 103 is adapted to hold a medical treatment device, such asone containing a therapeutic radiation source. There are severalmanufacturers of such equipment, and the design of the structure and pod103 in particular will be as universal as is economically possible toallow for the incorporation of as many different makes and models of thetreatment device as possible. In general, the average machine weighs18,000 pounds and bolts to a base plate such as base plate 310. Thebolts that hold the machine are at one end of the machine and the bulkof the weight is at the other some ten feet forward of the boltsyielding a significant moment of torque. A steel base frame isincorporated into the steel frame of pod 103 to accommodate this torque.The frame is sufficiently rigid such that regardless of any bending ortwisting during transit, when the frame of pod 103 is placed on aprecision leveled foundation, the machine will be level to within themanufacturers specifications. Other electrical equipment including acontrol console, modulator rack, power transformers, and power filterscan also be mounted within pod 103. Wiring conduits are built into theframe to service the electrical equipment.

[0069] Pod 104 is substantially a mirror image of pod 102 with a fewminor exceptions. Pod 104 fits in between pods 103 and 105, and does notinclude a vault door. In addition, whereas portion 222 of pod 102included an exterior door, the equivalent portion of pod 104 can includeother amenities such as plumbing for a wash basin.

[0070] Pod 105 is substantially a mirror image of pod 101 although it iscontemplated that the equivalent portion to portion 212 of pod 101 willbe adapted for a different purpose, such as storage, restrooms, etc.

[0071] With reference to FIGS. 8 and 8B, pod 106 is one of four roofshielding containers to be placed on top of and perpendicular tofootprint pods 101 through 105. Each of the roof shielding containerscan be built with an outside dimension the same as a standard shippingcontainer. Pod 106 is placed at the rear of the modular unit. The bottomof pod 106 attaches to the top of the footprint pods 101 through 105.The side of pod 106 that attaches to pod 107 does not have a wall, butit includes a central rigid support between the upper and lower framesegments. When finished it can meet DOT regulations and codes, and becapable of being lifted from the end points by a container mover. It canalso be capable of being stacked five containers high with the othercontainers having a gross weight of 96,000 pounds each and be capable ofbeing shipped with a gross weight of 96,000 pounds. The shipping weightof the pod with the additional shielding and the roof support structuresbut without the radiation shielding fill material is preferablyconsistent with DOT shipping regulation for moving by truck withoutspecial permitting.

[0072] As is the case for all of the roof pods, there is no floor in pod106 in the area over pod 101 and pod 105 and over the shieldingcontainers in pods 102, 103 and 104 although there is a steel floor overthe treatment room portions of the footprint pods. In addition, there isa ceiling or roof covering all of pod 106 (as is also the case for allthe roof pods). When filled with radiation shielding material the totalweight of the fill could be 243,200 pounds with approximately 5.3 poundsper square inch of weight on both the shielding in the lower pods and onthe floor in the existing areas of this pod. The lateral force on theside walls could be 115,520 pounds. The lateral force could beapproximately 5.3 pounds per square inch occurring near the bottom ofthe pod. The wall material and thickness and supports should chosen tosupport this exemplary load or any particular load depending on theapplication. Access ports can be placed at appropriate intervals toallow a vacuum pump to fill and empty the container of the shieldingmaterial. In particular, access ports 325 can be provided along the roofas a series of spaced apart holes with normally closed spring loadedcovering flaps through which access to the interior space of the roofpods can be selectively provided.

[0073] Pod 106 is supported by the four steel supports 120 in pods 101and 105. It is constructed to span pods 102, 103 and 104 without bowingor placing any undue stress on these three pods, and includes a pair ofI-beams 320, 321 to distribute the load on the steel floor to supports120.

[0074] Pod 107 is another of four roof shielding containers to be placedon top of and perpendicular to the footprint pods 101 through 105. It isplaced in front of and adjacent to pod 106 at the rear of the modularunit. The bottom of pod 107 attaches to the top of footprint pods 101through 105. The side of pod 107 that attaches to pod 108 also does nothave a wall, which helps to minimize gaps and/or radiation leaks throughthe roof. Pod 107 attaches to the five footprint pods and to pod 106 and108. There will be no floor in pod 107 in the area over pod 101 and pod105. When filled with radiation shielding material the total weight ofthe fill could be 243,200 pounds with approximately 5.3 pounds persquare inch of weight on both the shielding in the lower pods and on thefloor in the existing areas of this pod. The lateral force on the sidewalls could be approximately 115,520 pounds. The wall material andthickness and supports should be chosen to support this exemplary loador the particular load as determined by the application. Access portsare placed at appropriate intervals to allow a vacuum pump to fill andempty the container of the shielding material.

[0075] Pod 107 is supported by the supports 120 in pods 101 and 105. Itis be constructed to span pods 102, 103 and 104 without bowing orplacing any undue stress on these three pods, and includes four I-beamsto span pods 102 though 104 and distribute the load to the supports 120.

[0076] Pod 108 is one of four roof shielding containers to be placed ontop of and perpendicular to the footprint pods 101 through 105. It isplaced in front of and adjacent to pod 107 near the center of themodular unit unit. The bottom of pod 108 will attach to the top offootprint pods 101 through 105. One side of pod 108 will attach to pod107 and the other side will attach to pod 109. There is no floor in pod108 in the area over pod 101 and pod 105. When filled with radiationshielding material the total weight of the fill could be 243,200 poundswith approximately 5.3 pounds per square inch of weight on both theshielding in the lower pods and on the floor in the existing areas ofthis pod. The lateral force on the side walls could be 115,520 pounds.As discussed above with respect to the other pods, the wall material andthickness and supports should be chosen to support this exemplary load.Access ports can also be placed at appropriate intervals to allow avacuum pump to fill and empty the container of the shielding material.

[0077] Pod 108 is supported by the supports 120 in pods 101 and 105. Itis be constructed to span pods 102, 103 and 104 without bowing orplacing any undue stress on these three pods, and includes four I-beamsto span pods 102 though 104 and distribute the load to the supports 120.

[0078] With reference to FIGS. 9 and 9A, pod 109 is one of four roofshielding containers to be placed on top of and perpendicular to thefootprint pods 101 through 105. It will be placed in front of andadjacent to pod 108 near the center of the unit. The bottom 505 of pod109 will attach to the top of footprint pods 101 through 105. There isno floor in pod 109 in the area over pod 101 and pod 105 and over theshielding containers in pods 102, 103 and 104. When filled withradiation shielding material the total weight of the fill could be243,200 pounds with approximately 5.3 pounds per square inch of weighton both the shielding in the lower pods and on the floor in the existingareas of this pod. The lateral force on the side walls could be 115,520pounds. As described above with respect to the other pods, the wallmaterial and thickness and supports should be chosen to support thisexemplary load. Access ports can also be placed at appropriate intervalsto allow a vacuum pump to fill and empty the container of the shieldingmaterial.

[0079] Pod 109 is supported by the supports 120 in pods 101 and 105. Itis be constructed to span pods 102, 103 and 104 without bowing orplacing any undue stress on these three pods, and includes I-beams 520,521 to span pods 102 though 104 and distribute the load to the supports120.

[0080] Pod 110 is a utility area that will be one of the five roof pods.Pod 110 will be placed on top of and perpendicular to pods 101 through105. Pod 110 will have several rooms built into it. These rooms will befor utility areas and will be built to be consistent with local buildingcodes for electrical, telephone, plumbing and other utilities asrequired.

[0081] It is envisioned that pod 110 could also be supported by supportsplaced in pods 101 and 105. However, it is envisioned that since pod 110would not contain the radiation fill material, the load of pod 110 wouldbe substantially less than the load of any of pods 106 through 109 andthus can be supported in any conventional fashion.

[0082] In one variation of the modular structure the medical device canbe removed and replaced after the structure is completed in a simple andefficient manner. This variation involves modifications to pods 103 and109 such that the portion of pod 103 containing the medical device andany associated control system can be removed and replaced while theremainder of the structure and the majority of the radiation fillmaterial remains in place.

[0083] Turning now to FIGS. 10 and 11, pod 103 a, which is a modifiedversion of pod 103, is depicted. Pod 103 a includes radiation fillsection 402 that is separated from the radiation treatment room 50 bylead shield 403. The removable portion of pod 103 a includes thetreatment room portion 404, barrier portion 420 and control room portion406. The treatment room portion 404 includes the base plate that wouldbe coupled to the medical device and is removable with respect totreatment room portions 410 and 408. The control room portion 406includes the associated control equipment and electronics and iselectrically coupled to and integral with portions 420 and 404.

[0084] The barrier comprising portions 416, 418 and 420 in pod 103 a canbe filled with radiation shielding fill material. Portions 416 and 418are relatively fixed and would normally remain filled with shieldingmaterial even during the medical device interchange operation. Thecenter barrier portion 420 is part of the removable section of pod 103 aand can be evacuated of its radiation fill material as necessary toremove and replace the medical device. The walls of radiation fillportions 416 and 418 abutting portion 420 are reinforced to contain theload of fill material when portion 420 is evacuated.

[0085] The associated electronic controls for the medical device areincluded on portion 406, which is adapted to be slid out betweenportions 412 and 414. While each of sections 404, 420 and 416 arepreferably coupled together, they could be separately removable. Inaddition rollers or other slide assisting means are preferably providedunder the removable sections so that the removable section of pod 103 acan easily be decoupled and removed and replaced.

[0086] In addition provisions can be made to stop the flow of fillmaterial from the roof sections above portion 420 as the removableportion of pod 103 a are removed. Turning now to FIGS. 12 and 13, pod109 a, which is a modified version of pod 109, is depicted. Pod 109 a issubstantially identical to pod 109 save the centralized trapezoidalportion 450 which is located to cover portion 420 in pod 103 a. Portion450 is constructed of reinforced steel and has access ports to both filland evacuate portion 450 of radiation fill material when removablesection of pod 103 a is to be removed. The lateral sides of portion 450are constructed to contain the load of the remaining radiation fillmaterial in pod 109 a from falling into portion 420 during medicaldevice removal and swapping.

[0087] As can be appreciated by those of skill in the art when providedwith the present disclosure, the modular structure can be formed bysequentially placing and connecting the pods in proper alignment. Tofacilitate construction and alignment of the pods, adjacent pods can beprovided with quick locking and/or aligning devices and/or the pods canbe connected in any conventional fashion. For example adjacent sides oftwo pods can be provided with a post and receiving hole to align withthe respective post or receiving hole of the adjacent pod.

[0088] Turning now to FIG. 15A, a representative connection between thelower rails 92 of a pair of footprint pods is illustrated. Alignmentpost 515 of rail 92 a is received in the hole 516 of rail 92 b, and thetwo rails are secured by a bolt and locking washer assembly 530.

[0089] Turning to FIG. 15B, a representative connection between thevertical posts 94 at the corners of adjacent pods is illustrated. Post94 b, including wall section 511 b, is connected with long bolt assembly531 to post 94 a, including adjacent wall section 511 a.

[0090] Turning now to FIG. 15C, an interior wall connection betweenadjacent pods is illustrated. Adjoining rails 96, or equivalently wallsupports 202, are connected by bolt assembly 532. One or more of therails 96 can include a reinforced wall portions, such as wall 303. (SeeFIG. 7)

[0091] As shown in FIG. 15D, the rails 96 a and b (of adjacent pods)holding ceiling panels 540 a and b are connected in similar fashion asare adjacent interior wall portions. The ceiling panels 540 a and 540 bcould be the ceiling over the central treatment area 50, or the ceilingpanels could serve as the roof over the entire structure, as would bethe case in the respective connection between pods 106 and 107.

[0092] Turning to FIG. 15E, a representative connection between aninterior portion of pod 101 with the door gusset 540 of pod 102 isillustrated. A representative wall panel 510, reinforced with support202, is secured to a portion of the door gusset 540 with a standard boltassembly.

[0093] Turning now to FIG. 15F, a representative connection between theends of a roof pod with the outside walls of pods 101 and 105 isdepicted. The upper frame rail 96 from the outside wall 510 of afootprint pod receives a bolt assembly holding the lower beam 92 formingthe bottom of a roof pod, such as pod 107. A spacer 550 can also beincluded between the pods.

[0094] Turning now to FIG. 15G, a representative connection between anI-beam in the roof pod and the roof support in the footprint pod isdepicted. I-beam 321 (see FIG. 8-8B) is connected through the floor ofthe roof pod and into a top flat portion of the support 120 (see FIG. 3)with a bolt assembly.

[0095] In addition while each radiation fill material containing sectionof each of the individual pods can include their own access port orports for filling and removing radiation fill material, in oneembodiment only the roof pods have access ports. In this embodiment theaccess ports can be along the top roof section of the roof pods andradiation fill material provided into those roof pods can flow bygravity into the appropriate portions of the footprint pods 101 through105.

[0096] It is also envisioned that the modular structure can bedisassembled by sequentially decoupling and removing the pods. For theroof pods, the radiation fill material can be pumped out of or otherwiseremoved from the containers prior to lifting the pods. The footprintpods, since there is no floor in the barrier sections, can be lifted bytheir ends with the filler material being left behind. It may benecessary to rap the sides of the pods as they are being lifted toassure that the filler does not stick to the inside of the pods.Alternatively, the filler material can be pumped out of the footprintpods prior to their removal.

[0097] While in the preferred embodiment, the radiation shielding fillermaterial is sand or another solid flowable or granular radiationadsorbent material, other types of filler material can be used. Examplesinclude, without limitation, silica, dirt, lead, lead shot, steel, scrappieces (such as metal punch outs), and various combinations or mixturesof the above. Where the barrier region is made substantially fluid tightsuch as by providing a bladder and/or caulking throughout the barrierregion once the pods are constructed, the filler material can be aliquid (such as water) or a slurry (such as a flowable fill concrete).Furthermore, it is contemplated that the specific type of shieldingmaterial and the physical dimension of the barrier region can betogether varied and selected to provide the necessary radiationshielding based on a particular application and a particular radiationsource. As discussed throughout, the density of the fill material willdetermine at least to some extent the load on the walls of the barrier,and the walls can be constructed and/or reinforced as appropriate basedon the expected load and any applicable building codes or constructiontechniques.

[0098] While the structure illustrated herein is constructedsubstantially entirely from free-standing pods, it is contemplated thatthe pods could only form a portion of a treatment facility. For examplepods 102 and/or 103 could be provided wherein the remainder of thestructure and/or the barrier (i.e. that formed in the illustratedembodiment by the remainder of the pods) could be constructed by anybuilding technique now known or hereafter developed. For exampleportions of the structure could be transported as preformed butcollapsed portions that would be assembled and arranged around theplaced pods.

[0099] It is to be understood that the invention is not limited to thespecific features shown and described, since the means herein disclosedcomprise preferred forms of putting the invention into effect. Theinvention is, therefore, claimed in any of its forms or modificationswithin the proper scope of the appended claims appropriately interpretedin accordance with the doctrine of equivalents.

What is claimed:
 1. A modular structure for housing a radiation sourcecomprising: a plurality of free standing transportable modules connectedto form a central treatment area and a barrier substantially surroundingthe central treatment area, the central treatment area adapted for humanoccupation and to contain a therapeutic radiation source, the modulescomprising a support frame structure and at least one wall, the barrierincluding first and second spaced apart rigid walls and a quantity ofradiation shielding filler material contained between the first andsecond walls, the quantity of filler material sufficient tosubstantially reduce the measurable radiation level outside the centraltreatment area when a radiation source is placed in the centraltreatment area.
 2. The modular structure of claim 1 wherein at least twoof the plurality of modules each include portions of said first andsecond spaced apart rigid walls, the portions defining a channelcomprising a portion of the barrier.
 3. The modular structure of claim 2wherein the channels in the at least two modules are adjacent andsubstantially aligned.
 4. The modular structure of claim 3 wherein theadjacent channels are in fluid communication such that radiationshielding filler material provided into one channel can flow into theadjacent channel.
 5. The modular structure of claim 1 furthercomprising: a second plurality of free standing transportable modulesconnected to form a roof over the central treatment area.
 6. The modularstructure of claim 5 wherein: the roof includes a roof barrier above thecentral treatment area, the roof barrier comprising a rigid floorsupporting a quantity of radiation shielding filler material above thecentral treatment area.
 7. The modular structure of claim 6 wherein: thesecond plurality of modules include portions above the barrier formed bythe first plurality of modules, the portions above the barrier includinga quantity of radiation shielding filler material and comprising aportion of the roof barrier.
 8. The modular structure of claim 7wherein: the portions of the second plurality of modules over thebarrier formed by the first plurality of modules are in fluidcommunication with the barrier such that radiation shielding fillermaterial provided into the roof barrier can flow into the barrier. 9.The modular structure of claim 8 wherein: the weight of the secondplurality of modules and the roof barrier is substantially supported bya portion of the barrier.
 10. The modular structure of claim 1 wherein:portions of the plurality of modules define an area outside the centraltreatment area and the barrier, the outside area adapted to form roomssuitable for human occupation.
 11. The modular structure of claim 10wherein: the outside area comprises at least one wall and a floor. 12.The modular structure of claim 7 wherein: the first and second pluralityof modules each have a length not exceeding about 53 feet, a width notexceeding about 14 feet, and a height not exceeding about 13 feet 6inches.
 13. The modular structure of claim 12 wherein: each of themodules have a major axis defined along their length and the major axesof the first plurality of modules are substantially parallel to eachother and the major axes of the second plurality of modules aresubstantially parallel to each other.
 14. The modular structure of claim13 wherein: the major axes of the second plurality of modules aresubstantially perpendicular to the major axes of the first plurality ofmodules.
 15. The modular structure of claim 1 wherein: the plurality ofmodules are coupled to a foundation and the barrier abuts thefoundation.
 16. The modular structure of claim 12 wherein: the pluralityof modules comprise at least 3 modules.
 17. The modular structure ofclaim 16 wherein: the central treatment area comprises a portion of atleast one module and at least one module comprises a steel base framefor supporting a medical treatment device.
 18. The modular structure ofclaim 1 wherein: at least one module comprises a door providing accessto the central treatment area, the door comprising radiation shieldingmaterial.
 19. The modular structure of claim 18 comprising: radiationshielding panels between at least two of the modules, the radiationshielding panels comprising a portion of the barrier.
 20. A method ofconstructing a modular structure for housing a radiation sourcecomprising: forming a central treatment area sized and configured forhuman occupation and to contain a therapeutic radiation source,connecting a plurality of free-standing transportable modules to form abarrier zone substantially surrounding the central treatment area, thebarrier zone defined by at least first and second spaced apart rigidwalls comprising portions of the plurality of modules, delivering aquantity of radiation shielding filler material to the barrier zone toform a barrier substantially surrounding the central treatment area, thequantity of filler material sufficient to substantially reduce themeasurable radiation level outside the central treatment area when aradiation source is placed in the central treatment area.
 21. The methodof claim 20 further comprising: placing portions of at least two of theplurality of modules forming the barrier zone in fluid communicationsuch that radiation shielding filler material can flow between theportions.
 22. The method of claim 21 further comprising: connecting asecond plurality of free standing transportable modules to the firstplurality to form a roof barrier zone over the central treatment area,and delivering a quantity of radiation shielding filler material to theroof barrier zone to form a roof barrier above the central treatmentarea, the quantity of filler material sufficient to substantially reducethe measurable radiation level outside the central treatment area when aradiation source is placed in the central treatment area.
 23. The methodof claim 22 further comprising: placing a portion of the roof barrier influid communication with the barrier such that radiation shieldingfiller material provided into the roof barrier can flow into thebarrier.
 24. The method of claim 23 further comprising: providing thefirst plurality of modules with each having a length not exceeding about53 feet, a width not exceeding about 14 feet, and a height not exceedingabout 13 feet 6 inches.
 25. The method of claim 21 further comprising:forming a portion of the barrier zone with at least one of the pluralityof modules that includes portions of the first and second spaced apartrigid walls comprising the barrier, and wherein the walls of the atleast one module include rigid reinforcing members on the walls andrigid support members mounted between the walls.
 26. The method of claim25 wherein at least two of the plurality of modules have a longer sideand a shorter side, the method further comprising: connecting the longside of one of the plurality of modules to the long side of another ofthe plurality of modules to form the central treatment area.
 27. Themethod of claim 25 further comprising: supporting at least a portion ofthe lateral force load of the radiation shielding filler material on thewalls comprising the barrier zone with rigid support members mountedgenerally between the tops and bottoms of the walls.
 28. The method ofclaim 20 wherein at least one of the plurality of modules includes aradiation shielding door providing access to the central treatment areafrom an area outside the barrier.
 29. The method of claim 28 wherein: atleast one of the plurality of modules includes portions of the first andsecond spaced apart rigid walls comprising the barrier, the wallsincluding rigid reinforcing members and rigid support members mountedbetween the walls.
 30. An apparatus for forming a radiation treatmentcenter comprising: a plurality of free standing modules each comprisinga support frame and at least two spaced apart rigid walls defining achannel between the walls, the modules each having outer dimensionsgenerally defining a rectangular solid having a major axis, wherein themodules are adapted to be connected to each other to form a barrier zonesubstantially surrounding a central treatment area, the barrier zonecomprising the channels of the modules and wherein the channels of atleast two of the modules are in fluid communication such that radiationshielding filler material provided into one channel can flow into theadjacent channel, and a second plurality of free standing modules atleast one of which comprises a reinforced floor portion, the secondplurality of modules adapted to be placed on top of and connected to thefirst plurality of modules with the reinforced floor portions above andsubstantially covering the central treatment area, the second pluralityof modules having portions that would be aligned over and in fluidcommunication with the barrier zone such that radiation filler materialprovided into the second plurality of modules could flow into thebarrier zone.
 31. The apparatus of claim 30 wherein each of the moduleshave a length not exceeding about 53 feet, a width not exceeding about14 feet, and a height not exceeding about 13 feet 6 inches.
 32. Theapparatus of claim 31 wherein at least one of the plurality of modulesincludes rigid reinforcing members generally vertically mounted on thewalls and rigid support members mounted between the walls.
 33. Theapparatus of claim 32 wherein at least one of the modules includes agenerally open top above the channel of the module and a generally openbottom below the channel of the module.
 34. A transportable module forforming a structure comprising: a free standing transportable framestructure defining a bottom surface, a top surface and at least firstand second spaced apart side surfaces, a pair of spaced apart reinforcedrigid walls mounted to the frame and defining a channel space betweenthe walls, rigid supports mounted in the channel space between the wallsto resist lateral forces acting from inside the channel to force thewalls apart, wherein a substantial portion of the channel space betweenthe walls does not contain a ceiling or a floor such that the channelspace is open at its top and bottom such that granular fill material canbe provided into the channel space from above the top surface andentirely fill the channel space, and wherein the module is capable ofbeing lifted by its ends by a standard container mover withoutsubstantial deflection to facilitate construction of a structurecomprising a plurality of modules.
 35. The module of claim 34 wherein:vertically extending supports are mounted on the walls to provide thereinforcement.
 36. The module of claim 35 wherein: the frame structureand the walls could comprise steel.
 37. The module of claim 34 furthercomprising: a floor mounted to the frame structure outside the channelspace defined by the walls, whereby the floor containing portion issuitable for interior finishing into a finished room.
 38. An apparatusfor selectively blocking radiation through a doorway comprising: a doorand a retractable threshold adjacent the door, wherein the door and theretractable threshold each comprise radiation shielding material, alifting mechanism for raising the threshold when the door is closed andlowering the threshold when the door is open, wherein the thresholdblocks radiation leakage under the door when the door is closed andpermits substantially unobstructed access through the doorway when thedoor is open.
 39. The apparatus of claim 38 wherein a portion of thethreshold is above the bottom of the door when the door is closed. 40.The apparatus of claim 39 wherein the threshold retracts substantiallyunder its own weight when the door is opened.
 41. A modular structurefor housing a radiation source comprising: a plurality of free standingtransportable modules connected to form a central treatment area and abarrier substantially surrounding the central treatment area, thecentral treatment area adapted for human occupation and to contain atherapeutic radiation source, at least one of the modules comprising aportion of the central treatment area and including a support frame forholding a piece of radiation equipment in the central treatment area,the barrier including first and second spaced apart rigid walls and aquantity of radiation shielding filler material contained between thefirst and second walls, the quantity of filler material sufficient tosubstantially reduce the measurable radiation level outside the centraltreatment area when a radiation source is placed in the centraltreatment area.
 42. The structure of claim 41 wherein: the at least onemodule comprising the support frame comprises at least a first sectionincluding the support frame and a second section removably coupled tothe first section, wherein the first section can be removed from thesecond section to allow the radiation equipment to be removed from thetreatment area, the first and second sections comprising a portion ofthe barrier zone, and wherein the second section includes a wall betweenthe first section and a portion of the barrier zone in the secondsection for containing the radiation shielding filler material in thebarrier while the first section is being removed.
 43. The structure ofclaim 42 further comprising a second plurality of modules above thefirst plurality to form a roof barrier zone, at least one of the secondplurality of modules over the barrier zone of the first sectionincluding a floor member for holding radiation shielding filler materialin the roof barrier zone when the first section is being removed.